/**
 * Should objects be aligned by a bounding box?
 * [Bug] Scaled objects sometimes can not be aligned by edges
 *
 */
function initAligningGuidelines(canvas) {

	var ctx = canvas.getSelectionContext(),
		aligningLineOffset = 5,
		aligningLineMargin = 4,
		aligningLineWidth = 1,
		aligningLineColor = 'rgb(0,255,0)',
		viewportTransform,
		zoom = 1;

	function drawVerticalLine(coords) {
		drawLine(
			coords.x + 0.5,
			coords.y1 > coords.y2 ? coords.y2 : coords.y1,
			coords.x + 0.5,
			coords.y2 > coords.y1 ? coords.y2 : coords.y1);
	}

	function drawHorizontalLine(coords) {
		drawLine(
			coords.x1 > coords.x2 ? coords.x2 : coords.x1,
			coords.y + 0.5,
			coords.x2 > coords.x1 ? coords.x2 : coords.x1,
			coords.y + 0.5);
	}

	function drawLine(x1, y1, x2, y2) {
		ctx.save();
		ctx.lineWidth = aligningLineWidth;
		ctx.strokeStyle = aligningLineColor;
		ctx.beginPath();
		ctx.moveTo(((x1 + viewportTransform[4]) * zoom), ((y1 + viewportTransform[5]) * zoom));
		ctx.lineTo(((x2 + viewportTransform[4]) * zoom), ((y2 + viewportTransform[5]) * zoom));
		ctx.stroke();
		ctx.restore();
	}

	function isInRange(value1, value2) {
		value1 = Math.round(value1);
		value2 = Math.round(value2);
		for (var i = value1 - aligningLineMargin, len = value1 + aligningLineMargin; i <= len; i++) {
			if (i === value2) {
				return true;
			}
		}
		return false;
	}

	var verticalLines = [],
		horizontalLines = [];

	canvas.on('mouse:down', function() {
		viewportTransform = canvas.viewportTransform;
		zoom = canvas.getZoom();
	});

	canvas.on('object:moving', function(e) {

		var activeObject = e.target,
			canvasObjects = canvas.getObjects(),
			activeObjectCenter = activeObject.getCenterPoint(),
			activeObjectLeft = activeObjectCenter.x,
			activeObjectTop = activeObjectCenter.y,
			activeObjectBoundingRect = activeObject.getBoundingRect(),
			activeObjectHeight = activeObjectBoundingRect.height / viewportTransform[3],
			activeObjectWidth = activeObjectBoundingRect.width / viewportTransform[0],
			horizontalInTheRange = false,
			verticalInTheRange = false,
			transform = canvas._currentTransform;

		if (!transform) return;

		// It should be trivial to DRY this up by encapsulating (repeating) creation of x1, x2, y1, and y2 into functions,
		// but we're not doing it here for perf. reasons -- as this a function that's invoked on every mouse move

		for (var i = canvasObjects.length; i--;) {

			if (canvasObjects[i] === activeObject) continue;

			var objectCenter = canvasObjects[i].getCenterPoint(),
				objectLeft = objectCenter.x,
				objectTop = objectCenter.y,
				objectBoundingRect = canvasObjects[i].getBoundingRect(),
				objectHeight = objectBoundingRect.height / viewportTransform[3],
				objectWidth = objectBoundingRect.width / viewportTransform[0];

			// snap by the horizontal center line
			if (isInRange(objectLeft, activeObjectLeft)) {
				verticalInTheRange = true;
				verticalLines.push({
					x: objectLeft,
					y1: (objectTop < activeObjectTop) ?
						(objectTop - objectHeight / 2 - aligningLineOffset) :
						(objectTop + objectHeight / 2 + aligningLineOffset),
					y2: (activeObjectTop > objectTop) ?
						(activeObjectTop + activeObjectHeight / 2 + aligningLineOffset) :
						(activeObjectTop - activeObjectHeight / 2 - aligningLineOffset)
				});
				activeObject.setPositionByOrigin(new fabric.Point(objectLeft, activeObjectTop), 'center',
					'center');
			}

			// snap by the left edge
			if (isInRange(objectLeft - objectWidth / 2, activeObjectLeft - activeObjectWidth / 2)) {
				verticalInTheRange = true;
				verticalLines.push({
					x: objectLeft - objectWidth / 2,
					y1: (objectTop < activeObjectTop) ?
						(objectTop - objectHeight / 2 - aligningLineOffset) :
						(objectTop + objectHeight / 2 + aligningLineOffset),
					y2: (activeObjectTop > objectTop) ?
						(activeObjectTop + activeObjectHeight / 2 + aligningLineOffset) :
						(activeObjectTop - activeObjectHeight / 2 - aligningLineOffset)
				});
				activeObject.setPositionByOrigin(new fabric.Point(objectLeft - objectWidth / 2 +
					activeObjectWidth / 2, activeObjectTop), 'center', 'center');
			}

			// snap by the right edge
			if (isInRange(objectLeft + objectWidth / 2, activeObjectLeft + activeObjectWidth / 2)) {
				verticalInTheRange = true;
				verticalLines.push({
					x: objectLeft + objectWidth / 2,
					y1: (objectTop < activeObjectTop) ?
						(objectTop - objectHeight / 2 - aligningLineOffset) :
						(objectTop + objectHeight / 2 + aligningLineOffset),
					y2: (activeObjectTop > objectTop) ?
						(activeObjectTop + activeObjectHeight / 2 + aligningLineOffset) :
						(activeObjectTop - activeObjectHeight / 2 - aligningLineOffset)
				});
				activeObject.setPositionByOrigin(new fabric.Point(objectLeft + objectWidth / 2 -
					activeObjectWidth / 2, activeObjectTop), 'center', 'center');
			}

			// snap by the vertical center line
			if (isInRange(objectTop, activeObjectTop)) {
				horizontalInTheRange = true;
				horizontalLines.push({
					y: objectTop,
					x1: (objectLeft < activeObjectLeft) ?
						(objectLeft - objectWidth / 2 - aligningLineOffset) :
						(objectLeft + objectWidth / 2 + aligningLineOffset),
					x2: (activeObjectLeft > objectLeft) ?
						(activeObjectLeft + activeObjectWidth / 2 + aligningLineOffset) :
						(activeObjectLeft - activeObjectWidth / 2 - aligningLineOffset)
				});
				activeObject.setPositionByOrigin(new fabric.Point(activeObjectLeft, objectTop), 'center',
					'center');
			}

			// snap by the top edge
			if (isInRange(objectTop - objectHeight / 2, activeObjectTop - activeObjectHeight / 2)) {
				horizontalInTheRange = true;
				horizontalLines.push({
					y: objectTop - objectHeight / 2,
					x1: (objectLeft < activeObjectLeft) ?
						(objectLeft - objectWidth / 2 - aligningLineOffset) :
						(objectLeft + objectWidth / 2 + aligningLineOffset),
					x2: (activeObjectLeft > objectLeft) ?
						(activeObjectLeft + activeObjectWidth / 2 + aligningLineOffset) :
						(activeObjectLeft - activeObjectWidth / 2 - aligningLineOffset)
				});
				activeObject.setPositionByOrigin(new fabric.Point(activeObjectLeft, objectTop - objectHeight /
					2 + activeObjectHeight / 2), 'center', 'center');
			}

			// snap by the bottom edge
			if (isInRange(objectTop + objectHeight / 2, activeObjectTop + activeObjectHeight / 2)) {
				horizontalInTheRange = true;
				horizontalLines.push({
					y: objectTop + objectHeight / 2,
					x1: (objectLeft < activeObjectLeft) ?
						(objectLeft - objectWidth / 2 - aligningLineOffset) :
						(objectLeft + objectWidth / 2 + aligningLineOffset),
					x2: (activeObjectLeft > objectLeft) ?
						(activeObjectLeft + activeObjectWidth / 2 + aligningLineOffset) :
						(activeObjectLeft - activeObjectWidth / 2 - aligningLineOffset)
				});
				activeObject.setPositionByOrigin(new fabric.Point(activeObjectLeft, objectTop + objectHeight /
					2 - activeObjectHeight / 2), 'center', 'center');
			}
		}

		if (!horizontalInTheRange) {
			horizontalLines.length = 0;
		}

		if (!verticalInTheRange) {
			verticalLines.length = 0;
		}
	});

	canvas.on('before:render', function() {
		canvas.clearContext(canvas.contextTop);
	});

	canvas.on('after:render', function() {
		for (var i = verticalLines.length; i--;) {
			drawVerticalLine(verticalLines[i]);
		}
		for (var i = horizontalLines.length; i--;) {
			drawHorizontalLine(horizontalLines[i]);
		}

		verticalLines.length = horizontalLines.length = 0;
	});

	canvas.on('mouse:up', function() {
		verticalLines.length = horizontalLines.length = 0;
		canvas.renderAll();
	});
}

export default initAligningGuidelines;